1. Field of the Invention
The invention concerns an x-ray source of the type having multiple of electron sources separated from one another in a longitudinal direction, as well as an x-ray system with such an x-ray source.
2. Description of the Prior Art
Tomographic imaging x-ray methods (as are used for non-destructive materials testing, for example, but in particular in medicine) expose the examination subject to radiation from different directions. The individual projections obtained in this manner are subsequently calculated into a spatial image of the examination subject. The exposure of the examination subject from different directions is achieved by a movement of the x-ray source. For example, in computed tomography (CT) of the patient that is used in medicine, the patient is irradiated by an x-ray source rotating around the patient. Tomosynthesis is a further medical examination method with which a spatial image of the examination subject (in this case of the breast) can be acquired. In this special form of mammography, the breast is irradiated from directions situated in a limited angle range. In tomosynthesis the x-ray source is also moved relative to the examination subject.
However, movement of the x-ray source always entails technical problems. For example, given fast movement high inertial forces occur that the mechanical construction of the x-ray source must withstand. The x-ray source must typically be supplied with electrical power and cold water; both supply lines must follow the movement of the x-ray source or be strengthened so as to permit movement of the x-ray source by appropriate measures that are technically complicated, for example slip contacts or rotary transmission leadthroughs.
In order to avoid the need for movement of the x-ray source, the use of a stationary x-ray source having multiple of x-ray emitters (also designated as emitters for short) is proposed by J. Zhang et al. in “A multi-beam x-ray imaging system based on carbon nanotube field emitters”, Medical Imaging, Vol. 6142, 614204 (2006). The acquisition of tomographic image data sets is possible with such an x-ray source (also designated as a multifocus x-ray source) without a mechanical movement of the x-ray source being required. The examination subject is exposed with x-ray beams from different directions by the individual emitters of the multifocus x-ray source are excited to emission in chronological succession. In the course of an examination, the individual emitters are excited (activated) sequentially or even simultaneously to output an x-ray dose. If a detector that can be read out quickly is used in such a system, short scan times are possible.
In order to enable x-ray exposures with high resolution with short scan time of the examination subject, x-ray sources with high power are required. However, the power of known multifocus x-ray sources is limited by their thermal loading capacity. If this is exceeded, melting of the anode surface can occur. In order to avoid this and other consequences of thermal overloading, in conventional x-ray sources only low x-ray powers can be required by the individual emitters. Conventional multifocus x-ray sources are therefore limited to low amperages and short emission times.